10 Questions
What type of reaction is combustion, in terms of energy?
Exothermic
During a neutralization reaction, what happens to the temperature of the surroundings?
It increases
Which of the following is an example of an endothermic physical change?
Melting
What is the site where the reactants react in an acid-base reaction?
The system
During an exothermic reaction, what happens to the kinetic energy of the molecules in the surroundings?
It increases
What happens to the temperature of your hands when using hand sanitizer?
It decreases
What type of reaction is thermal decomposition, in terms of energy?
Endothermic
What is the role of water in an acid-base reaction?
It is the solvent
What type of reaction is photosynthesis, in terms of energy?
Endothermic
What happens to the energy of the surroundings during an endothermic reaction?
It decreases
Study Notes
Exothermic and Endothermic Reactions
- Exothermic reactions release energy to the surroundings.
- Endothermic reactions absorb energy from the surroundings.
Exothermic Reactions
- Chemical changes:
- Combustion: CH4(g) + O2(g) → CO2(g) + 2H2O(g)
- Neutralization: NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)
- Physical changes:
- Freezing: H2O(l) → H2O(s)
- Condensation: H2O(g) → H2O(l)
- Deposition: H2O(g) → H2O(s)
Endothermic Reactions
- Chemical changes:
- Photosynthesis: 6CO2(g) + 6H2O(l) → C6H12O6(s) + O2(g)
- Thermal decomposition: CaCO3(s) → CaO(s) + CO2(g)
- Physical changes:
- Melting: H2O(s) → H2O(l)
- Evaporation/boiling: H2O(l) → H2O(g)
- Sublimation: H2O(s) → H2O(g)
Reaction Systems and Surroundings
- In chemical reactions, the temperature measured is often that of the surroundings.
- The system consists of the reactants, while the surroundings include the solvent and everything around the reaction site.
Energy Transfer
- In exothermic reactions, energy is released as heat, increasing the kinetic energy of the surrounding molecules and the temperature.
- In endothermic reactions, energy is absorbed from the surroundings, decreasing the kinetic energy of the surrounding molecules and the temperature.
- Chemical potential energy is the energy stored in chemical bonds.
- Exothermic reactions release energy, resulting in lower potential energy in the products.
- Endothermic reactions absorb energy, resulting in lower potential energy in the reactants.
Identify and understand the difference between exothermic and endothermic reactions, including combustion, neutralization, freezing, condensation, and deposition.
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